In human adults, the initial encoding of visual information is carried out by the absorption of light by four kinds of receptors. These are the SWS, MWS, and LWS (short-, middle-, and long-wavelength sensitive) cones which serve daytime and color vision, and the rods, which serve night vision. The spectral sensitivities of these receptor types can be estimated by means of behavioral (psychophysical) studies in adults, using the technique of chromatic adaptation. We propose to study the functional development of the four receptor types in human infants 1 to 3 months of age. The forced-choice preferential looking (FPL) technique will be used in combination with chromatic adaptation. The major elements of the research are (1) Studies of light and dark adaptation in the infant rod system; (2) Construction of new equipment specialized for chromatic adaptation studies in infants; (3) Standardization of the equipment, and initial selection of spatial and temporal parameters, on adult subjects: (4) Chromatic adaptation studies, including both test-sensitivity and field-sensitivity, on infants; (5) Studies of the interactions of signals from the different receptor types, in infants; and (6) Studies of infants at risk for genetic color deficiencies ("color blindness").